How to open it for repairs or battery swap
The lamp opens up at the base: there are two smaller tabs next to the button, the semi-transparent plasic can be pressed in a bit with a knife, put a bit of paper inbetween to prevent the clip from snapping back. Next go with a knife towards one of the large tabs on the side until one side snaps out. Repeat for other side.
Remove the 4 screws (warning: 2x2 different types), out comes the pcb. Detach battery connector at the back.
remove two more screws to get at the battery
Overview of parts